Alireza Mahanfar

A Reconfigurable Patch Antenna Using Liquid Metal Embedded in a Silicone Substrate

A frequency-reconfigurable microstrip patch antenna is implemented using a stretchable silicone TC5005 substrate. The stretchable patch is fabricated by injecting liquid metal alloy Galinstan into a square reservoir fabricated in the silicone elastomer substrate. An aperture-coupled feeding method is presented to enhance the strain by separating the fixed feed element from the stretched radiating element. The implemented prototype is demonstrated to be stretchable by a strain of up to 300% (and the material has the potential for more). The electrical length of the patch antenna varies with the stretching, and we demonstrate frequency tuning from 1.3 to 3 GHz. A maximum radiation efficiency of 80% is measured for the antenna. The fabrication process of the antenna system and experimental results for impedance and radiation pattern are presented.

Reconfigurable Axial-Mode Helix Antennas Using Shape Memory Alloys

Reconfigurable structures based on smart materials offer a potential solution to realize adaptive antennas for emerging communication devices. In this paper, a reconfigurable axial mode helix antenna is studied. A shape memory alloy spring actuator is used to adjust the height of a helix antenna. With the total length of the helix wire fixed, the pitch spacing and pitch angle are varied as the height is varied. This in turn can alter the antenna pattern in order to adjust to altered operating conditions. In order to undertake the design, the Kraus equations for the axial mode helix are compared with simulation results, and their range of applicability is clarified. It is shown that based on these equations, antenna gain variation is possible by varying the height of the antenna, while keeping its conductor length fixed. We then show that a pattern can be reconfigured using a two-helix structure. Finally, a proof-of-concept helix antenna is implemented using a shape memory alloy actuator. Measurement results confirm that the pattern can reconfigure while maintaining a reasonable impedance match.

Mid-range wireless energy transfer using inductive resonance for wireless sensors

Methods are suggested and tested to measure and optimize the wireless energy transfer efficiency for mid-range (10–100cm) inductive coils with relatively low profile using magnetic resonance. These coils can be used to provide energy for wireless sensors and battery-operated devices. It is shown that for every system, a resonance frequency can be identified where the wireless energy transfer efficiency is optimal. Several prototypes are developed and tested as a proof of validity of the proposed technique. It is also shown that by tuning to the optimum resonant frequency and designing proper matching circuitry, an efficiency of about 25% for moderate profiles can be achieved.

Square Ring Antenna With Reconfigurable Patch Using Shape Memory Alloy Actuation

A pattern reconfigurable ring-patch antenna is presented. It comprises a bendable parasitic plate located in the middle of a fixed square ring. The fixed ring supports the feed, and the plate is effectively a parasitic structure. The plates bending action is from a bisecting hinge between the rectangular halves (flaps) that can be actuated separately. The actuation is by extending a shape memory alloy spring. The restoration is by decompressing the shape memory spring action using a parallel standard spring. The parasitic plate thus reconfigures with rectangular flaps which bend up, level, and down, relative to the ring plane. As a result of the reconfiguration, the pattern of the antenna is changed while the impedance match is maintained. Simulated and experimental results are presented for the pattern and impedance of a 100 mm × 100 mm square ring patch antenna prototype operating at 1.15 GHz. The effects of some geometric parameters on the pattern and impedance are investigated in order to analyze the pattern changing mechanism. A two-element array of the reconfigurable ring-patch antenna is presented that provides further de-correlation of the patterns.

Design Considerations for the Implanted Antennas

Different aspects of the design of implanted devices is discussed by numerical analysis of a conceptual model. Different antenna topologies are compared for their efficiency and sensitivity to variations in thickness and dielectric constant of a lossy superstrate (which models the skin). It was shown that microstrip patch and loop antennas are the most viable candidates among basic antenna topologies. A modified objective function is proposed which can take into account the strong detuning due to lossy superstrate. Finally the effect of a protective lossless superstrate is investigated intensive numerically. The trade-offs involved in the size of the protective superstrate are addressed by finding the trends in which the antenna performance varies with the dimensions of the protective layer.

Mechanically reconfigurable antennas using electro-active polymers (EAPs)

A class of electro-mechanically reconfigurable antennas are reviewed that use Electro-active polymer (EAP) actuators to move parts of the antenna including parasitic elements, thereby altering its parameters such as the radiation pattern. Compared to conventional methods such as switches and mechanical actuators, EAPs offer low cost, and high force-to-volume-ratios and are easy to manufacture. Advantages and limitations of different kinds of EAPs, i.e., ionic EAPs and dielectric EAPs, for reconfigurable antennas are discussed. Some possible actuator configurations including bending, hinge, and hemisphere forms are reported.

Self-Assembled Monopole Antennas With Arbitrary Shapes and Tilt Angles for System-on-Chip and System-in-Package Applications

The design, fabrication and measurement of self-assembled vertical and oblique monopole antennas, are presented. Vertical on-chip antennas offer advantages over conventional on-chip planar antennas, most notably potentially higher efficiency with associated superior coupling between distant and adjacent ports along the direction of the chip plane. The fabrication method enables lithographical specification of the monopole profile and its sloping angle so that the orientation and shape of monopoles can be controlled. The fabrication process uses SU-8 material and is performed under 200°C and is therefore compatible with many commercial microelectronic fabrication processes such as complementary metal-oxide silicon (CMOS) technology. This allows the integration of the antennas with CMOS front ends and other signal processing stages for communications or sensing.

Lithographic stress control for the self-assembly of polymer MEMS structures

We present a novel self-assembly mechanism to produce an assortment of predetermined three-dimensional micromechanical structures in polymer MEMS technology using lithographically defined areas of stress and mechanical reinforcement within a single structural material. This self-assembly technology is based on the tensile stress that arises during the cross-linking of the negative tone, epoxy-based photoresist SU-8. Two different thicknesses of SU-8 are used in a single compliant structure. The first SU-8 layer forms the main structural element and the second SU-8 layer determines the aspects of self-assembly. The second SU-8 layer thickness acts to both to create a stress differential within the structure as well as define the direction in which the induced stress will cause the structure to deform. In this manner, both the magnitude and direction of self-assembled structures can be controlled using a single lithographic step. Although this technique uses a single structural material, the basic concept may be adapted for other processes, with different material choices, for a wide variety of applications.

Beam-Steering Antenna using Bending Fluidic Actuators

A beam steering antenna is described which uses bending parasitic elements controlled by bending fluidic actuators (BFAs). The structure is a monopole antenna surrounded by four parasitic elements on a groundplane. The BFAs are controlled by linear controllers located below the groundplane. In this way, the parasitic elements comprise BFAs and the action of bending them away from the monopole to alter the mutual impedances is analogous to the reactance variation of switched parasitic antenna. When a parasitic element is not bent, it can act as a reflector or director for low-gain beam formation, while the other parasitic element is bent away from the monopole and hence not affecting the beam. Two configurations have been realized with different numbers of bent parasitic elements, and experimental results for these configurations are presented. Patterns with low cross correlations can be attained while keeping the return loss below a reasonable limit.

Polymer MEMS fabrication process for system-on-chip self-assembled millimeter-wave antennas

A novel micro-electro-mechanical systems (MEMS) fabrication process is developed to create self-assembled on-chip high efficiency antennas. A self-assembly technique is used to create out-of-plane on-chip antennas with excellent radiation efficiency on low resistivity substrates. This paper discusses on the fabrication of a monopole antenna and the measurement of the antennas radiation pattern characteristics. To achieve improved isolation and reduced loss, a thick dielectric layer was placed under the antennas and the transmission lines. The measurement shows maximum realized gain of -2.5 dBi at 66 GHz.